"rodeur" de condensateurs

[chm]

J' ai employé ce terme "large" un peu à la va vite.
Excusez moi ! Je pensais qu' il couvrait grosso modo la largeur de la bande audio d' un tuner.
Quel est le spectre de ce bruit ? Je ne comprends pas le -3db à 2KHz ! j' ai quasiment tout à apprendre, je sais !
Christophe

[alayn91]

Bonjour,

Ce spectre correspond au signal issue d'un transistor à piles, placé dans un boitier métallique ( cage de Faraday ).
Il est réglé en mono et le signal est pris sur la sortie casque.
Le niveau du signal jusqu'à 1kHz est de l'ordre de -30dB.
Vers 3kHz, le niveau est de l'ordre de -33dB, ce qui correspond à un niveau 2 fois plus faible.
On peut dire que le spectre de bruit de ce signal s'étend jusqu'à 3kHz.
Ce qui n'est pas très élevé !!

Sur ce site, tu peux générer différents bruits.
- http://mynoise.net/NoiseMachines/whiteN ... erator.php

Le bruit blanc généré par ce site:

CaptureBruit.PNG (42.6 Kio) Vu 4031 fois

Il monte plus haut en fréquence.

Le bruit blanc généré par Audacity:

CaptureBruitAudacity.PNG (63.51 Kio) Vu 4031 fois

Son amplitude est moins régulière.

Audacity est un programme prévu pour enregistrer, analyser, modifier et générer des signaux audio.

[6336A]

Le niveau du signal jusqu'à 1kHz est de l'ordre de -30dB.
Vers 3kHz, le niveau est de l'ordre de -33dB, ce qui correspond à un niveau 2 fois plus faible.

Tu es certain ?

[alayn91]

Bonsoir,
Effectivement, c'est -6dB, en tension.
Donc, ça nous donne 5kHz environ.

Alors, quelle source de bruit choisir ??

[lulrik]

Pour apporter mon grain de sel le rodage des condensateurs est nécessaire aussi en vidéo, un signal RGB d'une ColécoVision ne m'a donné le bleu que au bout de 10 minutes de fonctionnement

(je ne connais pas les fréquences des signaux vidéo RGB) je sais que c'est 15kHz pour la péritel mais de la à être certain que ça s'applique aussi pour le signal Bleu.

[alayn91]

Bonjour,
Si ta console a 30 ans, tu peux, peut-être, envisager de changer ce condo, et quelques autres !!
Ce n'est plus du rodage, ça.
C'est de la fin de vie.

[lulrik]

Bonjour,
Si ta console a 30 ans, tu peux, peut-être, envisager de changer ce condo, et quelques autres !!
Ce n'est plus du rodage, ça.
C'est de la fin de vie.

Je me suis mal exprimé ^^ c'était après un recapage, en revanche lors de la fin de vie, un condensateur me faisait des soucis de synchro.

[Pougatchoff]

.

Un lien intéressant sur le sujet:

http://www.nmr.mgh.harvard.edu/~reese/electrolytics/

The thin layer of aluminum oxide formed to insulate the capacitor foil constitutes formation. Capacitor manufacturers use proprietary mixes of chemicals and DC electricity to create this insulating layer, which deteriorates with time and idleness. Often the oxide layer is in such bad shape in older equipment that it must be reformed or else the capacitor will fail catastrophically. All methods of reforming use the slow reapplication of DC electricity to restore the oxide layer to its original thickness and uniformity. In my opinion, there's no one proven way to reform - many different approaches are available, but all have one element in common - slowness. The reforming must proceed faster than the buildup of heat due to the low resistance of the faulty oxide layer - this will at least take hours, and can take days.
Current-Limited Method (from Angela Instruments): Here's a link to Angela instruments's instructions for reforming old electrolytics out of their chassis using an external power supply. This method uses a large series resistor and a high-voltage power supply to reform capacitors that are NOS (new-old stock) or capacitors removed from the equipment's chassis.

Voltage-Limited Method 1: The voltage-limited methods use a handy device called the variable autotransformer (a.k.a. Variac, General Radio's brand name). Using a high-voltage external power supply, each capacitor is slowly brought up to working voltage by slowly raising the line voltage to the power supply. This can also be done with a variable DC supply with a range from about 50V to 500V, but variacs are cheaper and more common. A resistor can be placed in series to monitor the current, but watching the voltage also can reveal reforming progress; at each variac setting, the voltage will slowly rise until reforming at that voltage is complete.


It's easy to make a supply for this purpose from junk-box parts; the circuit is a pair of 500mA 24V transformers connected secondary to secondary, followed by a voltage tripling circuit. Total cost was about $10 (really), including the box from the local Radio Shack. Being a voltage tripler, regulation is weak and the voltage drops a lot as current increases. I've exploited this characteristic to give a rough estimate of the current drain, as shown in the chart on top of the supply. (The values were measured using a rheostat and my DMM - a supply using a different collection of parts would have similar behavior, but would measure differently). Typically I would connect my supply across the electrolytics to be reformed, along with my DMM set to its highest voltage setting. I plug my supply into the variac (turned off, set to zero), turn the variac on and slowly increase to the 30 volt setting. If the voltage reading on the DMM does not rise, or rises to less than 95 volts, there's likely a short. If the voltage rises, the voltage indicates the current drawn by the supply. As the capacitor starts to reform, the leakage current will decrease and the voltage will continue to rise. Once the leakage has decreased to an acceptable level, I go stepwise upward with the variac setting until the operating voltage for the capacitor is reached.

In the equipment's chassis, often capacitors of different voltage ratings are connected by voltage-dropping resistors, and the equipment uses the current demands of the circuit to keep voltages in operating range. You could disconnect each capacitor from the circuit and reform individually, or perhaps follow method 2.

Voltage-Limited Method 2: Using a two stage method, we can use the load of the circuit to keep the voltages in all the circuit's power supply capacitors within operating range. This is the method that I usually use, and can be carried out by using the equipment's own power supply. Look at the circuit and note the lowest voltage rating of all the capacitors that connect to the high voltage (B+) supply. Remove the tubes from the chassis and, using a variac, reform the power supply capacitors to this lowest voltage. Now put the tubes in the chassis and raise the highest-voltage-operating capacitor to this minimum voltage. This typically gives about 60% of the B+ and enough of the filament voltage to provide a load. Raise the line voltage slowly (using your variac) to reform the resistor-connected power supply capacitors each to its own working voltage (or slightly above).

This method has some more risk compared to reforming out of the chassis - you'll need to watch the total current draw and raise the voltage more slowly, since you have less information about the condition of the individual capacitors. Remember that it's quite likely that all of the connected capacitors except one will reform, but that one bad section will draw lots of current. You cannot assume that, if the acceptable leakage for one electrolytic is 1 mA, then it's ok for 4 electrolytics connected together to have leakage of about 4 mA - your group of 4 electrolytics must have a combined leakage less than that allowed for a single electrolytic otherwise you've allowed the possibility of 3 of good quality and 1 clunker.

If the equipment has a vacuum tube rectifier, you must jumper it with some silicon diodes for this method to work. It's really easy though - remove the rectifier and use some clip leads and a couple of 1N4007s as shown in this picture. WARNING - this method obviously leaves wires exposed while you work. These wires are potentially at HIGH VOLTAGES which can kill. For example, if you rest your right hand on the variac (ground) and touch the exposed clip leads, that will form a circuit from one arm, through your chest, and down through the other arm - potentially causing cardiac arrest. To me, this seems no more hazardous than working around live tube equipment with the covers off, though extreme caution is warranted in both cases. Proceed at your own risk!

Some final cautions:

Excess Current: you must keep a close eye on either the rate at which the voltage is rising, or you must measure the current directly while reforming. Either unsolder the connection between the rectifier and the capacitor and insert a current meter, or insert a resistor (while measuring the voltage across the resistor and calculating the current), or use the voltage drop across a resistor already correctly placed in the circuit to follow the current.
Vacuum Tube Rectifiers: These get their filament voltage from the same power transformer as the B+ supply. Thus, at the low initial voltages that you'd like to start the reforming at, they don't conduct. Observing the proper polarity, temporarily replace them with silicon diodes using an old tube base (with diodes soldered in place) or with diodes connected by clip leads.
Over-Fusing: To protect the power transformer while reforming, replace the usual 2 or 3 amp fuse with a very low value, such as 0.25 or 0.5 A. Your variac will prevent the turn-on surge that normally would open this sized fuse.
Over Voltage for the Capacitors: Be careful of the operating voltage when the tubes are removed from the chassis; without a load, the voltage delivered by the B+ transformer will be much higher than the normal operating voltage, and may exceed the capacitor's voltage rating.

[lulrik]

instructif merci

[alayn91]

Bonsoir,
Nul, aucun intérêt.